As with other electronics, as the demand for smaller, more versatile, and more powerful electronic devices has grown, CMOS (Complementary Metal-Oxide Semiconductor) devices have been reduced in size, and are being operated at increased speeds.
As CMOS fabrication technology advances, the lowered power supply voltage puts a severe limitation on power amplifier design in a radio transmitter because the maximum output power is primarily determined by supply voltage and load impedance. As CMOS technology scales, it becomes more and more difficult to deliver enough power from a single power amplifier due to the reduced power supply voltage.
Thus, the traditional single output power amplifier (PA) faces increasing challenges to deliver the required power.